Phthalocyanine pigments of the beta modification are well known in the art as green shade blue pigments used in a wide variety of applications including inks, coatings, plastics, and textiles among the others. Conventional methods for preparing pigments in the beta-form include subjecting the synthesis formed coarse-crystalline material (crude phthalocyanine) to either wet milling in the presence of milling aids and solvents, for example, salt attrition with glycols, or by dry milling without milling aids and with subsequent treatment with solvents or their mixtures with water. Once the pigment from these processes is dried, it can then be dispersed into water or solvent systems by known milling techniques, such as bead milling. Numerous modifications and combinations of these processes are also described in the technical literature. In general, these conventional methods have the disadvantages of being long multi-step procedures and thus very expensive and generating large amounts of wastewater.
U.S. Pat. No. 5,296,034 discloses copper phthalocyanine pigments and pigment preparations in the alpha-phase that are prepared by first wet milling a crude in the form of a water slurry at pH of 7-12 in a stirred bead mill operated at a power density more than 2.5 kW per liter of milling space followed by contact with a non-crystallizing additive and treatment with organic solvents such as alkanols. Despite the fact the process is quite short due to very aggressive wet activation step and the final material has good coloristic properties, the need to regenerate the solvent and isolate the pigment makes the process complex and expensive. To obtain the pigment in 100% beta-modification, the wet milling is carried out in aqueous isobutanol, as is described in U.S. Pat. No. 5,296,033.
U.S. Pat. No. 4,104,277 describes the process of the dry milling of a copper phthalocyanine crude followed by treatment of the activated material with emulsion of water, surfactant, liquid aromatic amine, and resin. The use of highly toxic amines in this process creates serious environmental problems.
Optionally, some esters, such a methyl benzoate, E.P. 0699720 A1, and dimethyl succinate, E.P. 0787775 A2, have been used as a solvent for an activated crude treatment. Upon completion of the pigmentation step, the solvent is hydrolyzed by heating the pigment slurry with caustic.
U.S. Pat. No. 4,158,572 describes a process of producing a β-modification phthalocyanine pigment composition by dry grinding a crude phthalocyanine, stirring the ground material with an aqueous medium containing a non-ionic surfactant and water soluble resin and isolating the pigmentary product. The required isolation in this process is an economic disadvantage, and in the course of the isolation, most of the surfactant is transferred into wastewater thereby creating an environmental problem.
U.S. Pat. No. 6,056,814 and U.S. Pat. No. 6,379,451 disclose pigment compositions that are produced by dry milling a crude phthalocyanine in the presence of a surfactant and a water-soluble resin. The resulting pigment composition is readily dispersed into an aqueous system to obtain aqueous pigment dispersion. Despite the fact the process is simple and the pigment composition easy dispersed, it is limited by systems based on acrylic resins. In addition, the shade of the composition and viscosity are difficult to control and the pigment is not stable against flocculation.